【作者】 王伟；

【导师】 张洪江；

【作者基本信息】 北京林业大学 ， 水土保持与荒漠化防治， 2011， 博士

【摘要】 优先流是一种快速非平衡的土壤水分运动过程。森林流域中优先流的发生可提高土壤水分有效性,减少地表径流形成,对流域森林水文过程具有重要影响,有利于水资源保护和调控。探讨不同环境条件下优先流与土壤基质的相互作用,揭示优先流形成机理是当今土壤学和水文学交叉部分亟待解决的重点和难点问题之一。本研究采用亮蓝溶液染色示踪与积水渗透试验相结合的方法,对三峡库区紫色砂岩地区广泛分布的阔叶林、针叶林、针阔混交林和灌丛等4种林地的土壤优先流过程进行观测,依据体视学原理,空间点格局方法和水分穿透曲线理论,分别对林地优先流的形态特征与发生类型,优先路径的分布状态和数量特征进行研究,揭示了紫色砂岩林地土壤优先流的形成机理。研究主要结论如下：(1)以体视学原理为基础,通过分析三峡库区紫色砂岩林地壤中流形态,发现土壤优先流多伴随基质流一同发生,其运移速率约为基质流的4-18倍。不同类型林地的土壤优先流发展过程具有一定差别,随土壤垂直深度增加,林地土壤优先流的空间异质性逐渐加剧。以染色路径宽度<10 mm和>100 mm为标准,参考水流运动形态变化状况,可将林地壤中流类型划分为：均质基质流、非均质指流、高相互作用大孔隙流、混合作用大孔隙流和低相互作用大孔隙流等5类,其中指流和大孔隙流均属于土壤优先流范畴。紫色砂岩林地土壤优先流主要以大孔隙流的形式产生和发展,一般发生于土壤10-20 cm深度位置并直达剖面母质层顶部。(2)采用点格局方法对三峡库区紫色砂岩林地优先路径的空间分布规律进行研究。结果显示在不同渗透水量条件下,半径25 cm的土壤剖面空间尺度范围内,林地优先路径整体上表现出了显著的聚集分布状态,且随着空间尺度扩大其分布状态具有向均匀分布发展的趋势。植物根系和优先路径的空间分布关系,在表层0-20 cm土壤范围内表现出显著正关联性,表土层优先路径的形成与植物浅根系生长密切相关；20-50 cm的中低层土壤中,紫色砂岩碎砾逐渐增多,植物根系数量减少,二者空间分布关联性逐渐降低；土壤剖面底层范围内植物根系与优先路径表现出了一定空间分布负关联性,可能是乔木垂直根系生长堵塞了土壤中原有裂隙所致。(3)紫色砂岩林地优先流染色区和未染色区内土壤水分穿透曲线特征具有显著差异,水分出流速率与穿透时间成显著对数曲线关系,未染色区土壤达到水分稳定出流阶段的时间较其对应的染色区土壤一般滞后5-10 s。通过土壤水分穿透曲线计算得到紫色砂岩林地土壤大孔隙当量半径可分为0.3-0.5 mm、0.5-0.7 mm、0.7-1.5mm和1.5-3.0 mm等4个级别,不同类型林地的土壤大孔隙数量具有一定差别,染色区和未染色区相同当量半径的土壤大孔隙数量相差了近一个数量级。土壤大孔隙数量与土壤饱和渗透率的相关关系随其孔径减小逐渐降低。染色区内较密集的大孔隙分布状况,促进了林地土壤优先流的发生,以及优先流空间异质性的产生。(4)林地土壤优先流的形成是通过外部因素和内部因素共同作用实现的。水分条件是优先流形成的外部因素,优先流形成的内部因素是与“植物-土壤”相关的环境因子。以Spearman相关分析结果为基础,筛选出土壤密度、砂粒含量、粉黏比、有机质含量、根孔数量、根重密度、根长密度、土壤初始含水量和渗透水量等13个环境因子进行主成分分析,结果表明土壤孔隙结构因素、土壤水分状况因素、土壤类型因素和外部降水因素等四个主成分影响着三峡库区紫色砂岩林地土壤优先流形成,其中土壤孔隙结构因素是林地土壤优先流形成的最重要因素,可解释其46.76%的方差变异。更多还原

【Abstract】 Preferential flow is a fast and non-equilibrium soil water movement process. Preferential flow in soils of forested watershed can increase soil water availability and reduce the genesis of surface runoff, which has an important influence on forest hydrological processes and is conducive to water resources conservation and regulation. Predicting formation mechanism of preferential flow and their interactions with the soil matrix under different environmental conditions has been identified as a key area where synergies between pedology and hydrology are urgently needed.Brilliant blue dye tracing and ponding infiltration methods were applied to observe preferential flow processes in four different forest soils (broadleaf forest, coniferous forest, mixed forest and shrub), which are widespread in purple sandstone regions of the Three Gorges Reservoir area. Based on the principles of stereology, spatial point pattern analysis and water breakthrough curves method, the morphological characteristics and occurrence types of preferential flow, the quantity and distribution characteristics of preferential flow paths were studied, respectively. The formation mechanism of preferential flow in forest soil of purple sandstone regions was revealed. The main results in this research were as follows:(1) Based on the principles of stereology, in purple sandstone forest soils of the Three Gorges Reservoir area, the morphological characteristics of interflow showed that preferential flow commonly occurred with soil matrix flow, and the water transport rates of preferential flow were 4 to 18 times faster than that of matrix flow. The preferential flow processes in different types of forest land were distinctive. The spatial variability of preferential flow in soils was gradually intensified with the soil depth. With stained path width<10 mm and> 100 mm as the criteria, and consulting water flow pattern changes, the forest interflow could be classified as five types:homogenous matrix flow, heterogeneous fingering flow, macropore flow with high interaction, macropore flow with mixed interaction and macropore flow with low interaction, which refers that fingering flow and macropore flow belong to preferential flow. Preferential flow in purple sandstone forest soils was mainly macropore flow, which generally occur at 10-20 cm depth of soil profiles and could reach to the top of parent material layers.(2) Point pattern analysis was used to reveal the spatial distribution of preferential flow paths in purple sandstone forest soils of the Three Gorges Reservoir area. The results showed that under different infiltration water volumes, with spatial scales in radius of 25 cm, the distribution of preferential flow paths was significant accumulation. Following the spatial scale expansion, preferential flow paths distribution trended to uniform. In the 0-20 cm depth soil surface layers, the spatial position of preferential flow paths and plant roots had a significant positive correlation. The formation of preferential flow paths in the surface soil layers was related to the growth of plant shallow roots. In the depth middle and deeper soil layers (20-50 cm), by purple sandstone debris gradually increased and amount of plant roots reduced, the spatial positive correlation of preferential flow paths and plant roots was decreases. In the bottom soil layers, the spatial distribution of preferential flow paths and plant roots showed a little negative correlation, which may be caused by the growth of tree vertical roots plugged original soil cracks.(3) Water breakthrough curves of soil samples in the dye stained area and the blank area were significantly different. The water effluent rate and its penetration time had a significant logarithmic relationship. The time of water effluent rate to stabilize in blank area was generally 5-10 s later than that in the dye stained area. The macropores in purple sandstone forest soils could be divided into four pore equivalent radius levels as 0.3-0.5 mm,0.5-0.7 mm,0.7-1.5 mm and 1.5-3.0 mm, respectively, which was calculated by water breakthrough curves. The quantities of soil macropores in different types of forest were distinctive, and macropores amounts in the dye stained area were 10 times bigger than that in the blank area. The correlation between macropore number and water stable effluent rates was dropped with the decreasing of macropores equivalent radius. More densely macropores distribution in the dye stained area promoted the formation of preferential flow, and generated its spatial heterogeneity.(4) Preferential flow occurrence in forest soil was attributed to external factors and internal factors. Water conditions were the external factors and environmental terms relevant to plant-soil were the internal factors. Thirteen environmental factors with higher Spearman correlation coefficient were selected for the principal component analysis, namely soil density, sand content, slit clay ration, organic matter content, root holes amount, root weight density, root length density, initial soil water content and infiltration water volume. The result showed that the soil pore structure factor, soil moisture factor, soil type factor, precipitation factor were the four principal components of formation mechanism of preferential flow in forest soils of purple sandstone regions, the Three Gorges Reservoir area. The soil pore structure was the most important factor with occurrence of preferential flow in forest soils, which accounted for 46.76% of the variance.更多还原